This invention relates to an apparatus for the manufacture of alkali metal halates. More particularly, it relates to a cell frame of the filter press design having means for positioning and holding anodes and cathodes in spaced relationship. Internal titanium intercell connectors hold the anodes to a molded synthetic organic polymeric electrolytic cell frame reinforced with such reinforcement materials as mica, asbestos fiber, calcium silicate or other suitable materials.
Alkali metal halates, e.g., sodium chlorate, can be prepared by electrolysis from alkali metal halide, usually purified to free it from heavy metals and from magnesium and calcium compounds. The formation of sodium chlorate by electrolysis of a sodium chloride brine solution represents a complex series of electrochemical and chemical reactions. The cell liquor product of electrolysis is concentrated, after which separation of sodium chloride and sodium chlorate takes place in a crystallizer. Final separation can be obtained in a batch centrifuge, and drying may be carried out in a heated air rotary drier, for example, after which the material can undergo grinding, screening, and packing operations.
The maintenance of a high operating efficiency depends upon a number of factors including temperature, pH, addition agents, and other factors. Chlorate cells generally have been constructed of iron tanks which are often completely lined with concrete. Such a steel-reinforced concrete chlorate cell is described in U.S. Pat. No. 3,401,109 to Anderson. Cell anodes are typically constructed of graphite or valve metals, and are immersed completely within the enclosing tank. Illustrative of such designs are U.S. Pat. No. 3,553,088 to Grotheer et al. and U.S. Pat. No. 3,676,315 to Goens et al. It is necessary to line the inside of such cells with a polymeric material or other nonconductive plasticized resin liner, such as polyvinyl chloride resin, polyvinylene chloride resin, polypropylene, or others. Such liners are described in U.S. Pat. No. 3,403,901 to Currey et al.
A difficulty commonly encountered with such lined concrete cell containers is their susceptibility to chemical attack in the corrosive environment of liquid and gaseous components typically present within a chlorate cell. Illustrative of corrosive materials present in the chlorate cell are concentrated brine (about 100-140 grams per liter); concentrated sodium chlorate solution (about 400-500 grams per liter); sodium hypochlorite solution (2-3 grams per liter); and gas with a chlorine content of about 0.5-3% chlorine, and an oxygen content of about 3%, all at a temperature of about 70.degree. C.
In addition, such tank-type chlorate cell structures are bulky and heavy, and require a substantial capital investment for fabrication and construction. Such tank-type cells have a fixed capacity, and lack any convenient means for adding to or reducing their operational capacity.